QUIETEST Performance Turbo Back Exhaust

2020MSMcivicSI

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IMO, the biggest exhaust problem with the 10th gen SI is that when you put a downpipe on it (especially catless), the volume is very hard to control, and it really doesn't matter what exhaust you have. Both stock and any aftermarket cat back... they all get too loud, raspy for a DD. (This is all based on sound clips... have not heard any exhaust in person)

So here is my SI full turbo back exhaust idea that should perform and be quiet:

1) 27won catless downpipe (3" -> 2.5")
2) 27won frontpipe (2.5" -> 2.5")
3) Vibrant Ultra Quiet Resonator #1141 (2.5" -> 2.5")
4) Borla S-Type muffler #40842S (2.5" -> 2.5")
5) Vibrant Streetpower muffler #1110 (2.5" -> Dual 2.25")
6a) Stock SI tip (for completely "sleeper" looking exhaust)
6b) Borla Resonated Exhaust Tips #20248 (2.25" -> 4")

All of above is ~$1000. Only cost left is an exhaust shop to make the 2.5" tubing and hangers to connect it all... I'm hoping that won't be too much (I do not have the skill or tools to weld so DIY is out).

I've done some measurements and I believe all this can fit in relatively "stock" locations. 1&2 above are exactly stock replacements. #3 will go right after the front pipe where there are already heat shields but only straight pipe (the type-r has a resonator here stock). #4 will go where the current SI resonator is (the stock resonator is almost the exact same size as the Borla muffler). #5 goes right where the stock SI system starts an upturn and then splits. #6a will definitely be easier to install but #6b should cut down on some more sound. If I did 6b, it will look a lot like the Greddy DDR exhaust (the exhaust tips are 12" long and 4" diameter).

The stock noise suppression is 1 huge cat, 1 resonator, and 2 mufflers in parallel. This would be 0 cats, 1 resonator, and 2 mufflers in series. (Don't know really if the resonated tips will do much).

There are 2 main reasons I don't just go ahead with this:
1) Maybe still too loud
2) I don't know a shop that I trust to weld this all together
Minor reason - don't want to hack up the stock exhaust just for the HDMI tip

So, does anyone have recommendations for a central OH exhaust shop? (Or at least one within reasonable driving distance)

Do you think this would actually get down to stockish DB levels? (Too quiet is a good problem to have IMO)

Is there anyone out there that has tried vibrant muffler with catless downpipe? (Couldn't find any audio clips) Or any combination of catless downpipe/muffler with no drone or rasp?

Should I keep the stock tip for a true "sleeper" look?

Sorry for the long post and feel free to build the above system and post sound clips here =)
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Hondanickx

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If you want quiet and something larger then stock the OEM type R exhaust is just that.
It's 2.38" OD with 18gauge wall thickness (60.5mm and 1.2mm wall) and goes to a double 2" muffler in the rear.I have one laying here and measured the sizes with a digital caliper.
Also there are a few that have the OEM type R exhaust with downpipe and to me that sounds perfect.
Eman has a sound clip from his si with type R exhaust.
 
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2020MSMcivicSI

2020MSMcivicSI

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Pretty sure the Type-R and SI exhaust are the same size after the front pipe. Type-R has larger downpipe and frontpipe. The Type-R exhaust also has a neck down at the front pipe connection to 2" and that is the most restrictive part of its exhaust. (All 10th gen civic have this neck down)

Its also not exactly easy to get a Type-R exhaust... almost all of them for sale are on the west coast and shipping is a nightmare.

Still keeping my search alive for a sound clip of catless and any muffler that keeps the 1.5 in quiet mode.
 

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I think your biggest issue is the cat. Like you said, it's massive and does more to quiet the exhaust than anything else.

I think an aftermarket catted DP with the stock exhaust, or the stock DP with an aftermarket exhaust, would sound good to your ears. Obviously there are performance trade offs to both of those options.

If neither of those appeal, try your idea. But with a catless DP I bet you'll still hear some rasp, especially if you're looking for it. Ultimately less restrictions = higher performance = more noise. So you need to decide the best balance.
 
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2020MSMcivicSI

2020MSMcivicSI

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The largest reason I want to go catless is to take advantage of the timing techniques for traction control. Basically you tune the car will pull timing rather than fuel to limit power and keep the front tires on the edge of traction better. When you pull timing and not fuel, a rich condition occurs and the cat will burn up the fuel that is extra. This makes the cat run hotter than it should.

In the long run, the cat will eventually melt together and make blockages and after enough time start to choke the engine. I know this from experience on my WRX... I melted the primary cat (it had 3 cats).

The traction control in this car is WAY TOO restrictive and really sucks the fun out of it... even in "off" mode. I have not done the petal dance yet but that is crazy for DD. The timing pull is a much better way of limiting power and keeps the turbo spinning to provide power again once traction is there.
 


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Pretty sure the Type-R and SI exhaust are the same size after the front pipe. Type-R has larger downpipe and frontpipe. The Type-R exhaust also has a neck down at the front pipe connection to 2" and that is the most restrictive part of its exhaust. (All 10th gen civic have this neck down)

Its also not exactly easy to get a Type-R exhaust... almost all of them for sale are on the west coast and shipping is a nightmare.

Still keeping my search alive for a sound clip of catless and any muffler that keeps the 1.5 in quiet mode.
Afaik the SI exhaust is 2" OD. The small bottleneck thing is just some BS 27won is trying to sell which doesn't make any sence at all.The bottleneck on the Type-r exhaust is (2.15") or 54mm OD and 2" ID and is about 2" long.(which could easly be removed also)
Afaik the SI exhaust is 2" OD.So it doesn't make sence that a 2.38" exhaust becomes a 2" exhaust all over because of a small bottleneck .
You could then also say that their 80mm downpipe is actually a 2.5" downpipe cause that's the smallest diameter....

Anyway to each their own ,i would use a Cat to keep the noise down ,a good designed cat doesn't take away any hp.
 
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2020MSMcivicSI

2020MSMcivicSI

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Anyway to each their own ,i would use a Cat to keep the noise down ,a good designed cat doesn't take away any hp.
According to this thread, the SI is larger than the other civics (other than Type-R).
https://www.civicx.com/forum/threads/si-exhaust-oem-pipe-size.12772/post-334910

It amazing how hard it is to search for simple information like this... too many different versions of civic and then each is changing diameter too much...

But I'm not chasing 5 HP or whatever the difference is with going catless... I just don't want to melt the thing (see my previous post).

I'm going to go under my car tonight and measure... but I do know some of it is oval which complicates things a little.
 

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According to this thread, the SI is larger than the other civics (other than Type-R).
https://www.civicx.com/forum/threads/si-exhaust-oem-pipe-size.12772/post-334910

It amazing how hard it is to search for simple information like this... too many different versions of civic and then each is changing diameter too much...

But I'm not chasing 5 HP or whatever the difference is with going catless... I just don't want to melt the thing (see my previous post).

I'm going to go under my car tonight and measure... but I do know some of it is oval which complicates things a little.
Too many People measure with something that isn't accured enough.
That Guy said the si exhaust was 2 3/8 before and 2.5"after.That would make it larger then a type R exhaust which is 2 3/8".

The oval section only Starts at the and before it splits into 2 X2".
The stock ex-t muffler also has a 2" inlet and only has a 1 5/8" exit tailpipe that tapers up again to 2".
I would love to see some acurate measurements with a caliper of the SI exhaust.
 
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2020MSMcivicSI

2020MSMcivicSI

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I would love to see some acurate measurements with a caliper of the SI exhaust.
This will happen either tonight or tomorrow. I'm supposed to play golf tonight but it looks like its going to be rained out... if the rain out happens, I'll get the measurements done tonight... might even get them done after golf anyways. Worst case is that I'll get them done tomorrow. I don't think I'll need to drop the exhaust to measure anything (only going to measure OD) but that will be the only thing that will stop me from getting good results.

I think my caliper is accurate to 0.01"
 


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2020MSMcivicSI

2020MSMcivicSI

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I took a shot in the dark and decided to build this exhaust., but couldn't use the resonated tips because there was just not enough room. (the tips would have stuck out past the bumper 6 inches)

So I guess bending stainless is just crazy and almost nobody does it... closest shop I found that would bend stainless was over 3 hour drive away. Everyone would just use aluminized... with Ohio winters, would prob last less than 5 years.

Because of this I went more of a DIY route where I hacked up the stock exhaust piping and had a friend weld the pieces in place (these are not the best looking welds in the world but they get the job done and since I couldn't get a custom stainless made, this works for me)

The only aluminized sections in the exhaust are the transition from oval to round right before the long muffler and between that muffler and the stock exhaust tip. I have the exhaust off right now and will be painting all the welds and those aluminized sections with high temp spray paint to prevent rust.

I will be taking some sound clips too this week... the sound is so much better than I thought it would be. The best words I can use to describe it is "civilized" and "mellow". For me, this is exactly what I wanted... something that sounds good but does not attract unwanted attention. Very, very little drone and really its not drone at all, just the sound of the exhaust but its really only noticeable when cruising 80+ mph and I don't do that much.

Had to bend the stock exhaust tubes out and use little section to flair out more, the mufflers 2 outlets were just wider than the 2 tubes on the stock tip. You can also see the oval to round section that bends upward (as installed on the car). This is to keep ground clearance the same as stock.

Honda Civic 10th gen QUIETEST Performance Turbo Back Exhaust Exhaust01


Here the stock exhaust is just cut and the borla muffler added. Also the stock resonator was removed and the vibrant ultra quiet added in same spot.

Honda Civic 10th gen QUIETEST Performance Turbo Back Exhaust Exhaust02


Today is unfortunately the coldest day in central OH since summer started so I am waiting for temps to get high enough to apply the paint. Will be doing 2 applications about 1.5 hours apart.
 
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2020MSMcivicSI

2020MSMcivicSI

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Very excited to hear this, also just realized you're local!
Yeah I'm on the east side of CBus... I'm thinking I'll have the audio clips done tomorrow, Wednesday at the absolute latest.

First coat of paint done:
Honda Civic 10th gen QUIETEST Performance Turbo Back Exhaust Exhaust03
 

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Nice insights, hope the new setup goes well for you!

From trying various exhaust setups myself, I can confirm that the factory DP is also the biggest "resonator" when it comes to controlling the overall volume in the cabin, and outside. My muffler delete was ok for 14 months until I added the 27won Catted DP and FP; after that it was horrible the 3 days I had it before switching to the Magnaflow Exhaust. Since then I've had the Invidia R400, and now the AWE Touring which comes with it's own FP.

Magnaflow I would say was pretty family-friendly, and could suit your needs if looking for a chill exhaust. Invidia was a bit boomy IMO, it was hard to drive with the windows down without getting your ears blown out from the bass, especially in a Coupe. AWE Touring is the loudest I would personally go with any aftermarket DP, passengers may or may not like it depending on preference; with the factory DP there's no concern with the AWE Track or Touring.

I also like the full 27won setup, Vincent and the team tuned it to accept their Catted and Catless DP options so it's still family-friendly on all counts.
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